In prior known bidirectional multiplex section switched self-healing ring transmission systems (also referred to herein as bi-directional line-switched rings (BLSRs)), bridging and switching, in the presence of a fault, was restricted to switching at the BLSR nodes which border to the fault. A problem with such an arrangement, in long distance networks, is that the restoration path can be extremely long. In certain applications, for example, transoceanic BLSR transmission systems, the length of the restoration path would be looped and may cause signals to traverse the ocean three times for particular fault conditions making the path extremely long, causing long delays and degraded system performance. The long delays and degraded service is extremely undesirable.
The notion of eliminating BLSR restoration path delay is not a new one, prior U.S. Pat. No. 5,341,364 entitled "Distributed Switching in Bi-directional Multiplex Section-Switched Ring Transmission Systems" by Marra et al., issued on Aug. 23, 1994 provided one solution to the problem. However, the method described in this patent has the disadvantage that it may not be compatible with conventional BLSR nodes, since it explicitly relies on the absence of BLSR loopbacks at the nodes bordering the failure. BLSR compatibility is important for at least two reasons: the first is mixed-vendor operation, and the second is software upgrades. What is needed is a method and apparatus which eliminates BLSR node restoration path delay yet which is compatible with existing BLSR loopback operation.